The present invention relates generally to exhaust gas recuperation, and more particularly to plate-type gas-to-gas heat exchangers for exhaust gas heat recovery, particularly in boilers and other combustion processes.
A variety of heat exchangers and heat recovery systems, utilizing liquid-to-liquid and gas-to-gas heat transfer media, are known in the process of recuperation. In the gas-to-gas application, the process of recuperation uses the exhaust gases from combustion to heat a combustion or charge gas, thereby extracting heat that would normally be lost when releasing the exhaust gases, which significantly improves the overall thermal efficiency of the associated system.
Other prior plate-type heat exchangers utilizing gas as the heat transfer media often have limited operational flexibility, resulting in low throughput of the heat exchanging gases. There tends to be a decrease in thermal efficiency because of the co-current and cross-current gas flow designs, resulting in less heat transfer. Also, turbulent flow within the heat exchangers tend to result in higher pressure drops in the heat exchanger. Further, it is also found that the use of stacked plates, with the space between plates carrying the associated gases in a counter-current rather than in a co-current design, enables the heat exchanger to operate at a higher efficiency, and therefore more economically. Therefore, there exists a need for a plate-type gas-to-gas heat exchanger which is particularly suited for laminar flow that increases thermal efficiency with decreasing throughput.
Another problem associated with plate-type heat exchangers is that, in an effort to channel the exhaust gas across the plate, guiding structures are placed along the plate, oftentimes with sharp angular regions that are not conducive to the exhaust gas flow. Consequently, because the exhaust gas is a product of combustion and contains particulate and other undesirable matter, exhaust gas particulate deposits on the exhaust plate along these regions, causing particulate build-up, pressure loss for the exhaust gas, and potential fouling of the exhaust gas plate.
Another problem associated with gas-to-gas plate-type heat exchangers is that condensation is created because the exhaust gas, during the process of heat transfer, is cooled beyond the dew point for the exhaust gas. The orientation and plate design of other heat exchangers does not provide for the proper management of this condensate formed as a result of the cooling of the exhaust gas, and this results in undesirable pressure drops. Often, carbon dioxide needs to be neutralized from this condensate to prevent corrosion during the heat exchange process. Typical plate-type designs do not allow for convenient collection of condensate to facilitate neutralization or disposal.
Additionally, in expensive applications such as steam and hot water boiler systems, it is desirable to be able to introduce a heat exchanger that can be utilized with existing products, if desired, rather than replacing the entire system if heat recuperation is desired. Therefore, a need exists for retrofit-type heat exchanger that can be added on with currently installed devices, as well as integrated into new device construction, if appropriate.
Therefore, it would be desirable to have a heat recuperation system that solves the aforementioned problems.
The present invention provides a plate-type heat exchanger for exhaust gas heat recovery that overcomes the aforementioned problems.
In accordance with one aspect of the invention, an exhaust gas heat recuperation system for use with a boiler is provided. The system includes a heat exchanger for exchanging heat from an exhaust gas to a charge gas. An exhaust gas inlet conduit connected to the heat exchanger is used for conducting the exhaust gas from the boiler to the heat exchanger, and an exhaust gas outlet conduit connected to the heat exchanger is used for conducting the exhaust gas from the heat exchanger to a suitable vent to atmosphere. Similarly, a charge gas inlet conduit is connected to the heat exchanger for conducting the charge gas to the heat exchanger, and a charge gas outlet conduit is connected to the heat exchanger for conducting the charge gas away from the heat exchanger. A boiler connected to the charge gas outlet conduit receives the charge gas when the charge gas exits the heat exchanger to assist boiler combustion.
In accordance with another aspect of the invention, an integral boiler and exhaust gas heat recuperation system is contemplated wherein the heat exchanger is connected directly to the boiler to form an integral unit, and further includes a condensate collection chamber connected to the heat exchanger for collecting condensation formed as a result of cooling the exhaust gas.
In accordance with another aspect of the invention, a gas-to-gas heat exchanger for exchanging heat between an exhaust gas and a charge gas is provided. The heat exchanger includes a plurality of exhaust gas plates, and each exhaust gas plate has a plurality of raised contoured ridges. The contoured ridges form a substantially sinusoidal path along each exhaust gas plate and define multiple substantially sinusoidal exhaust gas channels. The exhaust gas channels direct the exhaust gas therealong. The heat exchanger further includes a plurality of charge gas plates which are stacked alternately with and parallel to the exhaust gas plates. Each charge gas plate has a plurality of raised contoured ridges. These contoured ridges form a substantially sinusoidal path along each charge gas plate and define multiple substantially sinusoidal charge gas channels. The charge gas panels direct the charge gas therealong. The exhaust gas plates and the charge gas plates are connected together to permit exhaust gas entering the exhaust gas contoured channels to flow parallel to and in a substantially opposite direction to the charge gas flowing in the charge gas contour channels. The arrangement facilitates heat transfer from the exhaust gas to the charge gas.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.